The limited role of localized convective storms in runoff production in the western Negev Desert

High-scale floods in the Negev Desert are usually linked to rains originati ng from the Red Sea Trough (RST), characterized by high-intensity rainspell s. While the effect of the RST storms was assessed in the southern, central and eastern parts of the Negev, almost no information exists as to their p ossible impact in the western parts of the Negev. Rain characteristics and its role in runoff production were studied during the years 1989-1994 in the Nizzana research site in the western Negev Deser t. Only 7 out of 49 rainstorms (greater than or equal to 1 mm) originated f rom the RST, and only two of these seven storms produced runoff. While the RST-induced runoff accounted for only 3.9% of the total runoff in Nizzana, it accounted for 83.5-100% of the total runoff of four major ephemeral stre ams in the eastern part of the Negev. It is suggested that the limited role of the RST in the western Negev and its major role in flood formation in t he eastern Negev may contribute to stream capture of formerly westward flow ing streams eastward into the Dead Sea. A positive feedback mechanism is th us suggested. Whereas the topography may enhance atmospheric instability an d hence high convective rainstorms, the resultant floods may enhance rift w idening which in turn will foster atmospheric instability. (C) 2000 Elsevie r Science B.V. All rights reserved.